The reparation, adornment, and prosthetic extension of proteinaceous structures, namely, human fingernails and toenails and livestock hoofs, has been a common practice for centuries. Fingernails are currently known to be coated with multicolored nitrocellulose lacquers, repaired with cyanoacrylate adhesives, and extended with the use of acrylic monomer and polymer slurries or doughs that cure by peroxide/amine free radical mechanisms. The nitrocellulose-based lacquers currently in wide use possess the resiliency and toughness to perform this function well. However, such lacquers require very strong and pungent solvents to solvate the nitrocellulose. Thus, there have been several attempts to provide water-based polishes as substitutes for nitrocellulose-based lacquers. Both nitrocellulose-based lacquers and water-based formulations suffer to varying degrees from premature failure as decorative nail coatings. Such failure can take the form of wear at the tip of the nail, chipping from the ends and sides of the nail, to scratching anywhere on the nail. All three modes of failure are the result of catastrophic failure of adhesion between the nail polish and the nail plate (i.e., the proteinaceous substrate).
While cyanoacrylate adhesives for fingernail repair are relatively adherent to a fingernail plate, the acrylic materials employed for the purpose of creating an artificial fingernail prosthesis are not. Only after treatment of the fingernail surface with an unsaturated carboxylic acid, such as methacrylic acid (current commercial embodiments containing in excess of 70 percent methacrylic acid), will such acrylic monomer and polymer slurries or doughs adhere to the nail plate. Such harsh treatment on a relatively fragile surface poses a serious toxicological hazard due to the corrosive nature of the unsaturated carboxylic acids. Other unsaturated carboxylic acids presently being used in such applications include either alone or in part, acrylic acid and beta-carboxyethyl acrylate. Lower concentrations of these unsaturated acids pose a decreased danger to the intact fingernail surface; however, at such lower concentration the adhesion of the acrylic monomer and polymer slurry is minimized or lost completely. An analogous situation exists when attempting to repair a split or fractured hoof in that without the application of the corrosive and possibly toxic levels of unsaturated acids, very poor adhesion results.
Currently, the most widely used method for improving adhesion of nail polishes and prosthetic materials to proteinaceous substrates, such as fingernails and hooves, has been the physical abrasion and roughening of the proteinaceous substrate surface with a file, sand-paper-like, or other abrasive material, and/or the application of unsaturated carboxylic acid solutions (known in the artificial fingernail art as primers), followed lastly by the application of the polish or prosthetic material.
The disadvantages of such prior art adhesion-improvement methods include: (1) too much physical abrasion or roughening of the proteinaceous substrate, particularly a living fingernail, can be harmful to the substrate and surrounding cuticles; (2) in the area of hoof binding, cracks and fissures in the hooves are not readily abraded or roughened due to the inaccessibility of the surface to such abrasive materials and methods; (3) the unsaturated carboxylic acids that are often used (acrylic acid and methacrylic acid), either alone at full concentration of in combination with other diluents, are highly corrosive and can severely damage the protein of a fingernail or hoof or the underlying or surrounding living tissue; and (4) even with such harsh surface preparation as described above, the adhesive bonds obtained with such methods are poor and all too often inadequate to retain the polish or prosthesis for sufficient periods of time or under stress, thus causing the polish to chip and the prosthesis to break off in whole or in part.
Various prior art adhesive compositions and fingernail treatments have been suggested for improving the bond between coatings and the nail plate. For example, fingernail strengtheners deposited from solution are known, but do not improve bond strength. Materials and methods for obtaining high bond strengths to dentin, which is a partially proteinaceous substrate, have been described, but are the addition reaction products of, for example, pyromellitic acid dianhydride and 2-hydroxyethyl methacrylate (PMDM), the addition reaction product of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 2-hydroxyethyl methacrylate (BTDA-HEMA) and 4-methacryloxyethyltrimellitic anhydride (4-META). Such materials contain harsh unsaturated compounds and also exhibit inferior bond strength improvement compared to the present invention.
In general, prior art materials and methods suffer from a poor combination of toxicity, odor and/or poor adhesion-promoting performance.